1. Field of the Invention
The present invention relates to an apparatus and a method for deciding whether one signal level is coincident with another signal level or not.
Detecting or deciding elevation or coincidence of two signal levels is required in various fields. For example, the diversity reception system in a mobile communication system uses plural reception systems having little correlation with each other and has to select one of the reception systems that has a higher signal level than the other reception system. In such a case, it is necessary to detect elevation of the signal levels to change the reception systems and also coincidence thereof to start processes corresponding to detection of the coincidence.
2. Description of the Related Art
It is possible to detect the coincidence of two signal levels by using electrical devices, e.g., an analog to digital (A/D) converter, a digital comparator, etc. Namely, the A/D converter converts an analog input signal to a digital value of n bits. The digital comparator compares the digital values from two A/D converters and decides whether one digital value is coincident with another digital value or not.
However, the conventional system as described above has to use two A/D converters for two analog inputs, thereby a circuit scale of the system becomes large. Recently, the most significant priority for design of an apparatus is the miniaturization of the apparatus, therefore parts and circuit scale of the apparatus must be small in size. However, the system as described above cannot satisfy the requirement of the miniaturization.
Further, the A/D converter has an adjusting circuit for adjusting its full-scale and a zero-point so that the circuit of the system is larger by adding the adjusting circuit. Furthermore, there is a problem that it is not easy to match the tolerance between the A/D converters so as not to decrease their detection accuracy by addition of the adjusting circuit.